Note: Descriptions are shown in the official language in which they were submitted.
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SEALiNG COMPOUND
The present invention reiates to sealing compounds, particularly
sealing compounds suitable for use on container closures.
Back~ round
Seals for use on container closures, such as metal crowns, rolled
on caps or plastic caps are conventionally made from sealing compounds
based on a PVC-plastisol system. Such compounds are usually lined
into the closure as a liquid and fluxed to form the seal. Some seals
have been formed uslng a PVC-based compound in which the compound
is formed Into an extruded form such as pellets which are deposited
into the closure and shaped into the appropriate seal by means of a
die .
Seals for container closures, such as bottle caps, must have
specific characteristics in order to adequately seal a container. The
seal must be soft enough so as to adapt to any possible irregularities of
the container edge, such as a bottle neck, especially on a reused glass
bottle. Simultaneously, the seal must be adequately elastic to maintain
the seal between the closure and -the container, especially when the
container holds a pressurized product, such as beer or tonic. The
seals must also serve as barriers to the ingress or egress of water
vapor and oxygen. This is especially important in connection with the
keeping qualities of beer, which is adversely affected by oxygen.
Finally, the seal itself must not alter the taste of the packed product.
PVC-based compounds adequately fulfill these characteristics,
though the use of PVC has been objected to because of its waste
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disposal problems and in particular, because of the health
risks which have been claimed from the use of PVC on food
packs. There has therefore been an increased demand for
compounds which are free of PVC, yet have the same sealing
characteristics as PVC.
Some attempts have been made to make sealing
compounds based on polyethylene, -though they have not gained
any widespread acceptance due to their inferior characteristics
as compared to PVC-based compounds. Some characteristics have
been enhanced through the addition of various additi~es, but
the additives make the compounds so expensive that they are not
competitive or marketable.
Summary of the Invention
The present invention is a relatively inexpensive
sealing compound which is PVC-free and has excellent sealing
characteristics. The present invention is a polyethlene-based
compound containing selected elastomers and suitable fillers.
It is an aspect of the present invention to provide a
low cost, PVC-free sealing compound, preferably for use on
container closures, which contains either low density poly-
ethylene or linear low density polyethylene; a styrene-
isoprene-styrene block copolymer and/or a thermoplastic elas-
tomer mixture of an ethylene-propylene copolymer, such as EPM
or EPDM, EVA and process oil; fillers such as talc, calcium
carbonate, kaolin, titanium dioxide and mixtures thereof; and
cork powder.
It is a further aspect of the present invention to
provide a PVC-free sealing compound with similar or superior
sealing characteristics as PVC-based compounds.
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It is another aspect of the present invention to
provide a low density polyethylene based sealing compound hav-
ing a styrene-isoprene-styrene block copolymer, one or more
fillers and optionally cork powder.
A feature of the present invention is a PVC-free
sealing compound of linear low density polyethylene, styrene-
isoprene-styrene blocX copolymer and one or more fillers.
A further feature is to provide a polyethylene-based
sealing compound of polyethylene, such as low density po:Ly-
ethylene or linear low density polyethylene; a styrene-
isoprene-styrene block copolymer or a thermoplastic elastomeric
mixture of an ethylene-propylene copolymer and EVA and process
oil; and one or more fillers; the sealing compound being useful
in all applications in which PVC-based sealing compounds are
useful.
It is an advantage of the present invention to
provide an inexpensive, PVC-free sealing compound which has all
of the desirable sealing characteristics of PVC-based
compounds, but without the health and environmental disadvan-
tages of PVC.
The invention herein is a PVC~free sealing compound
of low density polyethylene or linear low density polyethylene;
styrene-isoprene-styrene block copolymer or a mixture of an
ethylene-propylene copolymer and EVA and process oil and one or
more fillers.
Further features and advantages of the present
invention will be apparent to those skilled in ~he art from the
descript on and claims below:
Description
The present invention is a sealing compound compris-
ng:
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a) from about 75 to abou-t 95 parts by weight of poly-
ethylene selected from the group consi.sting o~ low density
polyethylene and linear low density polyethylene,
b) from about 10 to about 20 parts by weight o~ (i) a
styrene-isoprene-styrene block copolymer, or (ii) a thermo-
plastic elastomeric mixture of an ethylene-propylene copolymer
and ethylene vinyl acetate copolymer and process oil, or (iii)
mixtures thereof,
c) from about 15 to about 50 parts by weight of one or
more fillers selected from the group consisting of talc,
calcium carbonate, kaolin, titanium dioxide and mixtures there-
of, and
d) from about O to about 15 parts by weight of cork
powder.
Low density polyethylene (LDPE) and linear low
density polyethylene (LLDPE) are known from the prior art, so
that no further information has to be given as to their
composition. For reasons of completeness in connection with
LLDPE, it is pointed out that it is not a pure polyethylene,
but a copolymer of polyethylene and a small amount of another
olefin, such as kaprylene (cf. U.S. Patent 4,076,698, which
gives a detailed description of LLDPE, and European Patent
Application 9376). A LDPE suitable in the present invention
has a melt index of 7 and a melting point of approximately
114C. A suitable LLDPE for the present invention normally has
a melt index of 3.8 to 5.0 and a density of around 0.915. An
example of a commercially available LDPE is ESCORENE LD 251*
available from ESSO. A commercially available LLDPE used in
the present invention is Grade 09-046*, from DSM sold by
Stamilex.
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The styrene-isoprene-styrene block copolymers used
according to the invention are linear polymers (also called
segmental polymers), in which the ends o-f polyisoprene chains
are in e~ch case terminated by polystyren~ segments (cf. U.S.
Patent 4,085,186, particularly column 4). Such block co-
polymers are commercially available with the tradenames
CARIFLEX TR-1107 (Shell), or EUROPRENE SOL T 190 (EniChem).
The styrene content of the commercially available block copoly-
mers varies from product to product, but is generally between
10 and 40%, so that the isoprene content is from about 60 to
about 90~. The aforementioned commercial products preferably
have styrene contents of 15 to 25~. I-t is important that the
hardness oE these block côpolymers is not excessive. 'rhus,
preference is given to those block copolymers with a Shore-A
hardness of 20 to 50 and preferably approximately 30.
The thermoplastic elastomeric mixture which may be
used instead of the block copolymer is a mixture of an
ethylene-propylene copolymer, such as EPM or EPDM and EVA and
process oil. Reference is made to European Patent Application
00 32 804 with reference to the thermoplastic elastomeric
mixture of substantially EPM or EPDM-elastomer, EVA and process
oil suitable in the present invention. Any liquid hydrocarbon
process oil is suitable. Process oils are well-known, and are
described, for example, in European Patent Application
00 32 804. A commercial product suitable for the purposes of
the invention is ESCORENE ULTRA EX 095* (by ESSO) wi-th a melt
index of 1.5 and a Shore-A hardness of approximately 58. These
mixtures are also known as elastomeric alloys.
*Trade-MarX
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The fillers useful in the present invention are well known to those
skilled in the art and are commercially available. A preferred filler is
talc, having a particle size of 75~1 (99% passes through a sieve with a
75 ,~ internal mesh diameter) . Other fillers include calcium carbonate,
kaolin ~also known as china clay or clay) and titanium dioxide.
Preferably the latter fillers are in a fine powder form, having a
particle size of 50"u (98 or more % pass through a sieve having an
internal mesh diameter of 50~u). Additionally, mixtures of these fillers
can be used in the invention. Other fillers, not specifically mentioned
herein, but well known to one skilled in the art, could be used in the
present invention so long as they do not adversely affect the desired
characteristics of the compound.
The amount of filler or fillers useq in the present invention ranges
from about 15 to about 50 parts by weight with a preferred range of
about 20 to about 40 parts by weight.
An optional, but preferred, ingredient of the present invention is
cork powder. Preferably, the cork powder has a particle size of about
75,u. The cork powder may be added in quantities from about O parts
by weight to about 15 parts by weight, with the preferred amount
being about 10 parts by weight.
The sealing compound may be made in any conventional manner.
The various ingredients are randomly mixed together to create a
blended, homogenous compound. The compound can be mixed in a
standard mixer, such as a Banbury mixer or in any other type of mixer
or btender which is normally used for making sealing compounds.
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Preferably, the compound is made by an extrusion/molding
technique in which the ingredients are fed in the correct proportions to
the head of the extruder which extrudes the formed compound.
Once the compound has been formed it may be used in any manner
similar to those currently in use with PVC-based compounds. For
example, dry mixture having a powder-like consistency can be used and
can be processed into webs or sheets under the effect of pressure.
These webs or sheets are then cut into small plates or disks which can
be introduced into closures as liners. These liners are preferably die
punched Into the final shape of the seal. Likewise, the dry mixture
may be introduced directly Into th~ closure and sultably heated and
compressed by a formlng die into the desired shape.
Preferably, the compound is extruded into pellets which are then
placed into the closures and formed into seals with a die. Examples of
such a process are well known in the PVC area, as evidenced by U.S.
Patent 3,696,956 and 3,883,025. These processes are as equally well
suited for the present sealing compound.
Another preferred process is to extrude the compound in a tape
form and cut plates or disks out of the tape for use as liners.
The sealing compounds of the present invention are particularly
suitable for use in container closures, preferably bottle closures, such
as crowns, rolled on caps and twist on caps. Such closures can be
made from tin plate, sheet steel or aluminum or plastic.
The following examples are presented to show the various types of
compounds which can be made under the present invention. These
examples are for illustration only and are not intended in any way
to limit the scope of the present invention.
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Example 1
A compound of the present invention was made of 85 parts by
weight of low density polyethylene having a melt index of 7; 15 parts
by weight of a styrene-isoprene-styrene block copolymer, sold under
the tradename EUROPRENE SOL T 190 by Enichem; and 40 parts by
weight of talc having a particle size of 75_~. The compound was mixed
and extruded into pellet form and formed in a closure by a cold die.
The sealing characteristics of the compound equalled those of the
presently availabie PVC-based compounds.
Example 2
A compound formed slmllar to that of Example 1, except llnear low
density polyethylene was used instead. The seals formed by the
compound showed very good sealing characteristics.
Example 3
A compound of 85 parts by weight of low in density polyethylene,
15 parts by welght elastomeric alloy, having a Shore A hardness of 58,
a vinyl acetate content of 1096 and sold under the tradename ESCORENE
ULTRA EX 095, and 40 parts by weight talc, similar to that of Example
1, was formed into seals and showed characteristics similar to those of
Example 1.
Example 4
A compound of 85 parts by weight of low density polyethylene; 15
parts by weight of elastomeric alloy, having the same properties as tha~
in Example 3, 40 parts by weight talc; and 10 parts by weight of cork
powder formed seals with sealing characteristics similar to those of
PVC-based compounds.
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While this invention has been described with reference to its
preferred embodiments, other embodiments can achieve the same result.
Variations and modifications of the present invention will be obvious to
those skilled in the art and it is intended to cover in the appended
claims all such modifications and equivalents as fali within the true
spirit and scope of this invention.
